1. Field of the Invention
The present invention relates, in general, to vehicles and, specifically, to variable displacement vehicle engines and more specifically, to vehicle drive trains.
2. Description of the Art
Vehicle engines are typically provided with an even number of combustion cylinders, i.e., 4, 6, 8, etc., even though certain engine designs with an odd number of cylinders, such as 5 cylinders, are also known. The amount of fuel/air injected into each cylinder is dependent upon the position of the throttle or accelerator pedal and determines the resulting power applied to the vehicle wheels and the speed of the vehicle. A preset fuel/air mixture is provided under idle conditions when the driver has disengaged his or her foot from the accelerator pedal.
It is known that fuel economy can be significantly improved by stopping the operation of some of the vehicle cylinders under light or partial load driving conditions. In such so-called "variable displacement engines," the injection of fuel into certain cylinders is stopped, with only the remaining cylinders continuing to operate. Various control schemes have been devised to determine the number of cylinders which are operating or rendered inoperable under various driving load conditions.
While variable displacement engines have proven to significantly increase fuel economy and, consequently to reduce fuel emissions, variable displacement engines create two objectionable problems. First, when a cylinder has ceased operation for a considerable period of time, the temperature of the cylinder wall and other surfaces within the cylinder drop as compared to the continuously operating, fuel burning cylinders. The cooler, inoperative cylinders are required under various power needs to suddenly resume operation when power demand increases. This can cause combustion inefficiency compared with the continuously operated, warmer cylinders and brings about a lower average fuel burning efficiency and an increase in fuel consumption and results in higher pollution exhaust gases from the colder operating cylinders. One approach to address this problem is to constantly shift which specific cylinders are working or nonworking under any load condition according to a preset sequence.
Another problem created by variable displacement engines is a result of inevenly spaced, intermittently operated cylinders anti creates objectionable torsional vibration in the passenger cabin as a result of an unbalanced engine operation when the engine is mounted in a conventional manner intimately connected to the cabin. Such vibrations have inhibited the use of variable displacement engine designs since the vibrations, when transmitted to the passenger compartment, are objectionable.
In a conventional rear wheel drive vehicle, power is transferred from the engine and transmission through a drive shaft to the rear axle and then to the two rear wheels. Since the engine is typically mounted in a conventional fore and aft manner on the frame via engine mounts or on an engine cradle or sub-frame intimately connected with the passenger cabin frame rails, any torsional engine vibrations are transferred from the engine to the passenger cabin or through the transmission and rear axle to the vehicle body via the rear wheels which are connected to the vehicle body by springs and shock absorbers. In addition, forces or shocks are transferred via the rear wheels to the passenger cabin as a result of uneven or rough transmission shifts as well as by shocks introduced on the rear wheel by rough pavement, potholes, etc. The end result of all of these forces which are transmitted to the passenger cabin is an uncomfortable ride for the vehicle passengers.
Torque tube type drive trains have been previously used on rear wheel drive vehicles. For example, a torque tube rigid to the rear axle was connected by a universal ball joint to the rear end of the transmission. The engine in this drive train was mounted to the vehicle by a pair of side positioned rubber mounts in an attempt to cushion engine torsional vibrations from the frame rails connected to the passenger cabin.
Thus, it would be desirable to provide a variable displacement engine which overcomes the problems associated with previously devised variable displacement engines. It would also be desirable to provide a variable displacement engine which maintains the temperature of inoperative cylinders at a minimum temperature suitable for efficient combustion and low pollution emissions when the inoperative cylinders are abruptly brought back into an operative state. It would also be desirable to provide a variable displacement engine with a unique drive train which isolates the torsional engine vibrations and other forces generated by the rear wheels of the vehicle from the passenger cabin. It would also be desirable to provide such a unique drive train which can be easily adapted to current vehicle rear wheel drive trains.